High performance adsorbents based on hierarchically porous silica for purifying multicomponent wastewater

Abstract

Hybrid hierarchically porous silica adsorbents were simply fabricated by the sol–gel method and modified with thiol or sulfonic groups. These materials with pores on both micrometre and nanometre scales exhibit a satisfactorily adsorptive property to various pollutants in water, including heavy metal ions (Hg²⁺, Cd²⁺, Pb²⁺, Cu²⁺, Ag⁺ and CrO₄²⁻) and organic compounds (dyes, biogenic amines, pesticides and amino acids). The thiol functionalized hierarchically porous silica micro-foam (SH-HSM), which has a low thiol content (0.66 mmol g⁻¹), shows significantly high adsorption capability to Hg²⁺ (140.1 mg g⁻¹) in particular. Then sulfonic acid-functionalized adsorbent (SO₃H-HSM) was obtained through direct oxidization of SH-HSM by H₂O₂ without destruction of the hierarchical structure. It was found that SO₃H-HSM could effectively remove organic compounds with positive charge in solution through electrostatic interactions. The adsorption capability of SO₃H-HSM for some basic dyes, such as fuchsin basic, could reach approximately 1145.2 mg g⁻¹. The mixture of SH-HSM and SO₃H-HSM showed good purifying capacity to simulate multicomponent wastewater, containing different inorganic and organic chemicals. The removal rate for any of the pollutants was more than 90%, and could even reach 100% for metal ions and dyes. The strong adsorption ability of these porous adsorbents may be due to the interwoven meso- and macroporous structures which can increase mass transport and easier accessibility for pollutants to the active sites.